1. Field of the Invention
The present invention relates to a screw with an improved head structure, and more particularly to a screw head having a driving socket capable of receiving, a square socket (Robertson) type driver a cross-recess (Phillips) type screw driver, and a flat blade driver. The present invention also relates to a punch for forming such a driving socket in a screw head.
2. Description of the Related Art
U.S. Pat. No. 5,358,368 to Conlan et al. issued on Oct. 25, 1994 discloses a screw having a driving socket capable of receiving a square socket (Robertson) type driver, a cross-recess (Phillips) type screw driver, and a flat blade driver. In this patent, as illustrated in FIGS. 8 and 9 of the drawings, the driving socket of the head 41 of the screw 40 includes a square recess 42 defined by four vertical walls 43 for receiving a square type driver, aligned slots 45 extending radially outwardly in alignment with two diagonally located corners of the square recess 42 for receiving a flat blade driver, and four grooves 44 extending diagonally outwardly from the corners of the square recess 42 to define a cross-shaped recess to receive a cross-recess type screw driver. The square recess 42 is deeper than the grooves 44 which, in turn, is deeper than the slots 45. Nevertheless, it is found that the driving socket tends to be damaged at the corner areas 46 when driven by a Phillips type screw driver.
U.S. Pat. No. 5,674,037 to Lu issued on Oct. 7, 1997 discloses a screw having an improved head structure. In this patent, as illustrated in FIGS. 6 and 7 of the drawings, the head 31 of the screw 30 includes a substantially cubic recess 32 defined by four sides 33, each of the four sides 33 having a short slot 34 extending perpendicularly outwardly therefrom, and a long slot 35 extending perpendicularly to two opposite sides of the cubic recess 32. The head structure disclosed by Lu is intended to solve the problem of the screw disclosed by Conlan et al. Nevertheless, it is found that the user may place a Robertson type driver in a wrong position indicated by the dashed-dotted square 50. As a result, the driving socket tends to be damaged at the corner areas 36 when driven by a power-driven square type socket driver. Namely, the problem encountered by the screw disclosed by Conlan et al. cannot be avoided completely.